Answer
Trains, telegraphs, and postage were deemed by Dalhousie as the "three great engines of social improvement" due to their transformative impact on society. Trains revolutionized transportation, enabling rapid movement of people and goods. Telegraphs facilitated instantaneous communication across vast distances, fostering social and economic connections. Postage, through its accessible and standardized system, democratized letter writing and enhanced communication. These advancements collectively fostered social progress, economic growth, and overall societal transformation.